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I have finally finished my M-38 project and have it on the road. The engine was completely rebuilt by a firm in which I have great confidence. When I drive it, I only start out with between 10 and 15 lb of oil pressure and it drops down to below 10 after it warms up to thermostate temp. I originaly did not rebuild the oil pump so I put a new set of internal parts in the pump. When I was taking out the pressure relief valve, the spring stuck, twisted and finally broke. The rebuild kit that I got did not have a pressure relief spring in it so estimated the amount of spring lost when it broke and placed a spacer in with the spring to make it about the same length. Now, it starts with a bit more than 10 lb pressure and maintains that pressure even when it warms up. My question (finally) is does the relief valve determine the level of pressure and if so does any one know where I can get a replacement relief spring?

I will try to post more photos of the finished product soon.

Thanks,

Steve H
M-38 61702

There's a very good site that explains the oil pressure thing quite well. I think Tony Norton posted it long ago on the G503 MB board. The short of it is the oil pump gears that establish the oil flow and the bearing clearances determine the developed oil pressure and the relief valve spring limits the max pressure by bypassing oil to the inlet side of the pump.

I always buy new complete pumps because the wear on the inside of the old pump housing reduces the efficiency of the new gear sets. I would guess most parts houses will stock the spring. Try Midwest Military, Turner or Bryan's.

Thanks for the great reference, Wes. After reviewing the items in the posting, I still believe that the pump is probably the problem. Your point about the wear in the pump housing could be the culprit. Before I replace the pump, I will try to get a new spring. I found it interesting that the factory actually put shims in with the spring to boost the pressure. That is why I think that the faulty spring may be part of the problem.

Again, thanks for you great advice.

Steve

I would not be racing out getting new things yet just replace the spring with the correct one...the factory fits shims to set pressure correctly and I would be checking oil pressure with a master gauge before assuming the oil pressure is low or out.

John is quite right here. A new spring and possibly a couple of shims and you may be back in business quickly.